1. Field of the Invention
This invention relates to an image heating device applied to an image forming apparatus, such as a copier, a printer or the like, and more particularly, to a device for heating an image utilizing a film.
2. Description of the Related Art
Conventionally, heat-roller-type fixing devices have been widely used as image heating devices represented by heating fixing devices. In such apparatuses, a tungsten halogen lamp is heated by passing current therethrough to heat a toner image via a roller.
Accordingly, there is some distance between a heating position and a toner, and therefore the efficiency of consumed energy is reduced.
In order to solve such a problem, image heating devices, such as one disclosed in U.S. Pat. No. 5,525,775, in which a heater is made in contact with a film to heat a toner image by the heat from the heater via the film, have been proposed, and an attempt to improve the thermal efficiency has been made.
Furthermore, as disclosed in Japanese Examined Patent Publication No. 5-9027 (1993) (Japanese Unexamined Patent Publication No. 62-150371), a heating device in which eddy currents are generated in a fixing roller by a magnetic flux to heat the fixing roller by Joule heat has been proposed. In this proposal, by making a heating position close to a toner by utilizing the generation of eddy currents, an attempt to improve the efficiency of consumed energy has been made.
In order to further improve the thermal efficiency, a fixing device in which a film itself or a conductive member provided in the vicinity of a film is heated by generating eddy currents therein to heat the film has been proposed.
In such film-type fixing devices, however, even if it is intended to increase the speed or the durability of the device, the film shifts in a direction orthogonal to the moving direction. If the amount of shift is large, an end portion of the film and the side plate of the fixing device rub each other, thereby damaging the end portion of the film in the longitudinal direction.
Particularly in image heating devices utilizing electromagnetic induction, since the film has a conductive (metallic) layer, a burr is produced at the end portion of the film, thereby causing crease or crack in the film and damaging the film.